Question

Consider the following statements in respect of slow sand filter and rapid sand filter:

1. The two filters differ in respect of the standards regarding the non-uniformity of the sand used in their filtering media.

2. The two filters do not differ in respect of the effective size of the sand used in them.

3. The two filters differ in respect of their respective under-drainage system.

4. The two filters differ in respect of their respective rate of filtration.

Which of the above statements are correct? 

1. 1, 2 and 3
2. 1, 2 and 4
3. 2, 3 and 4
4. 1, 3 and 4

Answer 1

Correct Answer - Option 4 : 1, 3 and 4

Concept:

The comparison of Slow Sand and Rapid sand filters with respect to concerning parameters are briefed in the following table:

Characteristics	Slow Sand Filters	Rapid Sand Filters
The effective size of filtering sand	The effective size of the filter sand ranges between 0.2 to 0.4 mm.	The effective size of the filter sand ranges between 0.35 to 0.55 mm.
Uniformity coefficient of filtering sand	The uniformity coefficient of the filter sand ranges between 1.8 to 2.5 or 3.0.	The uniformity coefficient of the filter sand ranges between 1.2 to 1.8.
Under drainage system	Laid in order to receive only filtered water. Generally, open jointed pipes or drains covered with blocks is be used	Laid in order to receive filtered water and also to pass water for backwashing. Generally, perforated pipe laterals or diffuser plate bottom are used.
Rate of filtration	Low, typically ranges 100 to 200 liters per hour per sq. m of filter area.	High, typically ranges 3000 to 6000 liters per hour per sq. m of filter area.

 

∴ Hence, statement 2 is incorrect, and the rest are correct.